Magnetoresistance and Orientation Function for Graphite Material with Axial Orientation

Abstract

Magnetoresistance of graphite materials measured at liquid nitrogen temperature is known to give information on graphitization degree and preferred orientation of the hexagonal carbon layers. This paper concerns magnetoresistance and orientation function for graphite material with axial orientation. We derived a mathematical relation between magnetoresistance and orientation function at first, assuming an orientation function for axial orientation to be propotional to the nth power of sine of the angle referred to an axis normal to the axial axis. Then, we defined three principal axes for the magnetoresistance, and related the components along these axes to the value of n. We obtained indirectly the full width at half maximum (FWHM) of the orientation function through magnetoresistance data. Comparison of the value of FWHM obtained indirectly with that measured directly by X-ray diffraction is important. For this purpose, we chose mechanical pencil lead as the sample for investigation, because it is known as one of the representative materials with axial orientation. We carried out measurements of magnetoresistance at liquid nitrogen temperature and orientation function by X-ray diffraction for the samples. The results obtained were very satisfactory.